The present invention relates to a rubber composition for a clinch comprising carbon black containing silica and a pneumatic tire using the same.
The clinch, which is the chafing part to the rim, is a tire component for receiving heavy load and extremely strong heat history and largely influences steering stability when driving. Therefore, a rubber composition, which has hardness high enough to endure heavy load, high stiffness and low heat generating properties, must be used for the clinch. Also, such a rubber composition must exhibit elongation at break (elongation properties) to a degree that chipping of the toe, which occurs when exchanging tires, does not occur. Furthermore, in recent years, in order to obtain fuel efficiency and reduced weight, simplification of the tire structure, thinning of the rubber gauge and reduction of weight of the cord are progressing and properties required in rubber compositions are becoming increasingly severe. Even for the clinch, a rubber composition having excellent steering stability when running and elongation properties in a balanced manner is desired.
With respect to clinch rubber, for which a great deal of properties are required, disclosed is the art of using polybutadiene rubber containing a syndiotactic component (see JP-A-7-118444). Also, instead of a single rubber composition, a multi-layer structure chafer obtained by joining several types of rubber having different compositions and properties has been invented (see JP-A-7-81335). However, multi-layering of the clinch and chafer rubber increases the load in terms of processes and invention of a clinch rubber composition having excellent balance of the above properties is an urgent task.
Usually, as a reinforcing agent that is compounded in rubber compositions for tires, carbon black and silica are used. However, when carbon black is compounded to a rubber composition alone, there is the problem that elongation at break becomes low and when silica is compounded alone, there is the problem that steering stability under severe conditions becomes poor. In order to compensate for the problems caused by compounding carbon black and silica alone, known is a rubber composition for a tire tread, in which both low rolling resistance and abrasion resistance are achieved by compounding a specific amount of a carbon black material containing silica to the tire tread part (see JP-A-2000-198883). However, this rubber composition is not intended for use as a clinch and a rubber composition for a clinch, which highly improves steering stability and elongation properties in a balanced manner, has not yet been obtained.